1. Field of the Invention
The present invention relates to a control system for an engine with an automatic transmission, and more particularly to an improvement in such a control system for reducing an engine output during a speed change operation of the automatic transmission and suppressing a speed change shock generated in the speed change operation.
2. Description of the Prior Art
Generally, in a vehicle including an engine capable of generated a large torque and an automatic transmission in combination, a speed change clutch of the automatic transmission is intentionally slipped for a long time in a speed change operation, so as to reduce a speed change shock of the vehicle generated in the speed change operation and also to reduce an impact force to be applied to a speed change mechanism in the automatic transmission. However, such a long-time slippage of the clutch promotes wearing of the clutch to cause a reduction in durability of the automatic transmission, for example. Thus, there is a problem in reliability of the automatic transmission.
To cope with this problem, there a technique has been proposed in Japanese Laid-open Patent Publication No. 59-97350, for example, wherein a speed change operation of the automatic transmission is detected, and an engine output is reduced by a predetermined quantity by retarding an ignition timing, for example, in the speed change operation detected above, thereby suppressing the speed change shock and shortening the slip time of the clutch.
In the conventional control system for the engine with the automatic transmission as mentioned above, as shown by a time chart in FIG. 2, engine output reduction control is not started immediately after a speed change operation command signal of the automatic transmission is generated. That is, after the speed change operation command signal is generated, a start timing of an actual shift operation of a speed change gear in the automatic transmission is detected as a timing when a turbine rotational speed of a torque converter or an engine rotational speed reaches an inflection point, and the output reduction control by output reducing means is started at the timing of reaching of the inflection point.
This is mainly due to the following reasons. Until the actual shift operation of the speed change gear is started after the speed change operation is started to operate a solenoid valve in a hydraulic system, a response lag Ta is generated due to a response lag of the hydraulic system. Furthermore, the response lag time Ta fluctuates due to deterioration by aging or the like. For this reason, the output reduction control of the engine is started at a timing when after the response lag time Ta has elapsed.
However, a response lag time Tc also exists due to a response lag on the engine side until the engine output is actually reduced by a predetermined quantity after starting of the output reduction control. Accordingly, in the conventional output reduction control where the output reduction control is started at the timing of detection of the inflection point, a start timing of an actual period of the output reduction is delayed from a start timing of a demanded period of the output reduction. Thus, these start timings cannot be made to coincide with each other, so that the speed change shock cannot be sufficiently suppressed.
If the start timing of the speed change operation is made to be in accord with the start timing of the output reduction control, another problem occurs in that an engine brake is generated upon shift-up in the automatic transmission at acceleration of the vehicle to slow down the acceleration of the vehicle since the response lag time Tc of the engine is shorter than the response lag time Ta of the automatic transmission.
To solve the above problems, a technique has been proposed in U.S. patent application Ser. No. 356,451 for deciding an engine output reduction period in a shift-up operation and a shift-down operation of the automatic transmission by providing a first predicting means for predicting an end timing of the shift-up operation on the basis of an engine rotational speed when the shift-up operation is detected, and a second predicting means for predicting an end timing of the shift-down operation on the basis of a time length from a timing of detection of the shift-down operation. However, the start timing of the engine output reduction period is given as a constant value considering the response lag of the hydraulic system in the automatic transmission. Accordingly, when the response lag time of the automatic transmission fluctuates due to deterioration by aging or the like, the start timing of the actual period of the output reduction is not certainly decided with respect to the start timing of the demanded period of the output reduction. As a result, the speed change shock cannot ),et be sufficiently suppressed.